Is this a head gasket problem?

I own a 90, auto, 4.0 Litre XJ,
I was coming home from a 700km trip, normaly during overnight trips, needle stays over the line before 100..at about 90,this time when aproching at the end of the trip needle was at about 95+.
When parked at home i noticed water leaking from under the car and propably from water pump....i asked my mechanic, he said that i would propably need a new water pump...ok till here !!!
He also told me that for a few days and if the leak wasnt major, i could use the car by filling water, i did that for few days cause i needed the car for a very serius reason, temperture NEVER gone to the red spot, but leaking has started to go big, and filling more and more frequently so i took the car by car assistance to mechanic.

He changed the pump with a new one filled the cooling system with paraflu and started the engine....when needle went just over 100....pressure at the water botlle was so much that a small crack was made....so leaking has started again, we fixed that, the mechanic said that i have "burn" a head gasket so air form cylinder was going to the cooling system...

Some more facts, car at idle was a bit like loosing rythm, car wasnt running very smooth, like had no power at mid revs....also we tried with less water and botlle cap open so we loose some preasure but water still over flowed... No water in oil ! No oil in water !!! No white smoke from exaust.

Please advice....is it only gasket? a crack in the head ? or something that i im not aware of ?

Have a compression check done on all cylinders. If they're all nearly equal and above 120psi, you don't have a leaking head gasket nor a cracked head.
Check the t'stat by putting it in a pan of water that's near to boiling point and see if it opens. It could be stuck closed.

well i guarantee that you have air in your system. and its a pain to get out. if your standing in the front of the jeep. all the way to the back right of the engine is the coolant temp sensor. unplug the sensor and start unscrewing it. with engine off. you will here a whoosh of air followed by coolant. that will purge your system. here is the write up.


http://www.olypen.com/craigh/cooling.htm

works great.

It is possible that you've got combustion gases entering the cooling system, however I believe it's unlikely since this problem arose right after the installation of a new water pump. Those closed systems are a ROYAL PITA to burp, it's probably just airbound.

Run the engine with the cap on the bottle, if the radiator hoses get rock-hard with pressure, it is very possible that you've got the cylinders pumping pressure into the cooling system.

If you're unsure, take it to another mechanic/shop for an opinion.

ohh i forgot....Thermostat was taken out, checked and it was working.... and left out...

You left the thermostat out? Why? That is usually a bad move, the engine needs the heat gained by a thermostat.

Eric

The crappy plastic tank is prone to cracks and leaks, especially if it's original. Changing the water pump might have yanked on the hoses enough to crack the nipple on the bottom. The plastic heater bypass valve also tends to crack and crumble when they are very old. It's not unusual to boil over if you still have air in the system or the cap is loose. Try loosening the temp sensor at the back drivers corner of the head and fill bottle until you get fluid coming out of the sensor hole.

I would pull the plugs and inspect them. Do a compression and/or leakdown test (look for bubbles in the coolant) if you're still thinking you have a bad head gasket.

use the link i posted it has instructions.

A BIG THANX from Greece !!!!

Thank you all guys, you just saved me about 1000 €, and the f unny thing was that i impessed the mechanic.
Anyway he did that with the valve and he also took out the air from cooling system from the coolant hoses...so "as he says"... be sure there is no air in it..., now the car works very good (checked in heavy traffic)...and we will install again the thermostat when weather gets more cold.

Only thing i need now is a coolant botle as mine is full of cracks and ready to leak...im thinkin to go and make a tailor made one form aluminium or stainless steel

Do a search. A few people have posted some sources for aluminum surge tanks (Moroso brand maybe?) and someone also mentioned some Volvos had metal tanks too. The nice part about a metal tank is that you get a real radiator cap and you can run a higher pressure which will cut down on boilovers as well. The stock tank cap is rated for 6psi, btw. The later, post 1991, open system ran 16-psi.

Tank from the Volvo 240 series is a fit for the closed cooling system RENIX Jeep. Probably more available over there than an oem replacement bottle and cap. Good luck.